I have BOINC manager on my PC set to use up to 400MB and to remove application from memory when the computing is suspended.
Rosetta takes about 1.5 GB and the only way to get rid of it is to KILL the processes.

Therefore I have removed Rosetta from task list.

I do not seek help, I just inform you before you piss off more people.

Well as the system requirements linked from the Rosetta home page ask for 1 GB of memory, trying to run with 0.4 GB is likely to cause you problems sooner or later.

Rosetta is a memory hungry application (due to the nature of the science) and most tasks will need at least 0.5 GB to complete.

If you were hitting 1.5 GB then you either hit a rare task with a very high memory load or you were running multiple Rosetta tasks at the same time. As your computer and task information is hidden from the public I can't see which of those two occurred.